Solder clad metal

ABSTRACT

THERE IS PROVIDED A THREE-COMPONENT COMPOSITE METAL STRIP MATERIAL FROM WHICH ARTICLES TO BE SOLDERED CAN BE PUNCHED, COMPRISING A STRIP OF READILY SOLDERABLY METAL SOLID-PHASED BONDED TO A STRIP OF NONSOLDERABLE METAL,   AND A LAYER OF SOLDER ADHERED TO THE EXPOSED SURFACE OF THE READILY SOLDERABLE METAL WHICH IS INLAID IN A GROOVE IN THE NONSOLDERABLE METAL.

'nited States Patent 3,720,503 SOLDER CLAD METAL George P. Trost, NorthAttleboro, Mass., assignor to Texas Instruments Incorporated, Dallas,Tex.

Original application Nov. 7, 1966, Ser. No. 592,579, now

Patent No. 3,482,303, dated Dec. 9, 1969. Divided and this applicationSept. 19, 1969, Ser. No. 871,230

Int. Cl. B32b 15/18 US. Cl. 29--191.6 1 Claim ABSTRACT OF THE DISCLOSUREThere is provided a three-component composite metal strip material fromwhich articles to be soldered can be punched, comprising a strip ofreadily solderable metal solid-phased bonded to a strip of nonsolderablemetal, and a layer of solder adhered to the exposed surface of thereadily solderable metal which is inlaid in a groove in thenonsolderable metal.

This is a divisional of application Ser. No. 592,579, filed Nov. 7,1966, now Pat. 3,482,303, dated Dec. 9, 1969.

Among the several objects of the invention may be noted the provision ofa method for manufacturing a solder-clad metal composite which does notrequire application and subsequent removal of a temporary stop-offmaterial in areas of metal which are not to be clad with the solder; theprovision of a method for manufacturing multilayer metallic memberscomprising a solderable metal layer having selected portions of thelayer clad with solder by a hot-dipping process and without requiringsubsequent removal of any stop-off material; and the provision of a cladmetal produced according to the methods of the invention. Other objectsand features will be in part apparent and in part pointed outhereinafter.

The invention accordingly comprises the constructions and methodshereinafter described, the scope of the invention being indicated in thefollowing claims.

In the accompanying drawings, in which several of various possibleembodiments of the invention are illustrated,

FIG. 1 is a sectioned trimetric view showing laminated strip material tobe partially clad with solder in accordance with the invention;

FIG. 2 is a cross section of the FIG. 1 material after it has beendipped in a liquid solder bath for solder-cladding;

FIG. 3 is a cross-sectional view showing the FIG. 2 material aftercertain portions of solder cladding have been removed;

FIG. 4 is an oblique view showing an article formed from the FIG. 3material;

FIG. 5 is a sectioned trimetric view showing a bimetallic member whichis to be provided with a solder coating according to a modified form ofthe invention; and

FIG. 6 is a section showing the FIG. 5 material after it has been dippedin a liquid solder bath for solder-cladding.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings. The drawings beingdiagrammatic do not show thicknesses to scale.

In order to clad a metal with solder, the metal to be used as a base isdipped in a bath of hot solder material until a quantity of the solderis deposited on the base. It is sometimes necessary that part of onesurface of the base shall not be clad with solder during its applicationto the base because it may jeopardize subsequent procesing operations orsteps. Therefore, a temporary stop-off material is usually applied tothe base to prevent solder from contacting and being coated onto thesurface covered by the stop-off material. The usual stop- 3,720,503Patented Mar. 13, 1973 off material must then be removed from the basemetal so that other processing steps can be performed on what was theshielded surface of the base metal. The present invention provides forthe manufacture of base metal clad with a solder layer wherein removalof stop-off material is unnecessary. The process provides clad metalsuitable for use in manufacturing certain articles, such as, forexample, base tabs used in the manufacture of transistors.

According to the present invention a strip 1 of base metal (FIG. 1)which is to receive a coating of solder is bonded to a base strip 3 of ametal which is either nonsolderable or which readily rejects solder.Metal 3 may be considered a permanent stop-off material in view of itsability to reject solder when immersed in a molten solder bath. Strips 1and 3 may be bonded together, preferably by solid-phase bondingtechniques, or liquid-phase techniques which will not melt at themelting temperature of the solder.

After strips 1 and 3 are bonded together they are dipped into a hot bathof liquid solder material. Some of the liquid solder adheres to thestrip 1 forms a layer 5 of solder on all exposed surfaces of strip 1.Strips 1 and 3 remain in the solder bath until the desired thickness ofsolder has been deposited on strip 1. Then the strips are removed fromthe solder. As shown in FIG. 2, the solder layer 5 comprises a wideportion designated 5a, which covers the upper surface of the strip 1,and other portions 5b and 50 which cover the side edges of strip 1.Portions 5b and 5c overhang the strip 3. None of the solder adheres tothe lower surface of strip 1 since it is shielded by the bonded strip 3.None of the solder adheres to the lower surface or side edges of thestrip 3 since the material used for strip 3 is nonsolderable.

Then the overhangingportions 5b and 5c of the solder layer 5 are trimmedoff along lines designated 7a and 7b which are flush with the side edgesof strips 1 and 3. The resulting clad metal article is shown in FIG. 3to comprise the stripsl and 3 and the portion 5a of the solder layer 5.Layer 3 is not removed '(as in the case of temporary stop-offs) butconstitutes part of the final product which is in the form of acomposite 1, 3 faced with solder 5a. Layer 3 may be a weldable metal sothat it can be used for welding to other items an article formed fromthe clad composite. For example, FIG. 4 illustrates a circular member 9punched from a clad strip such as shown in FIG. 3. This tab comprises aweldable but nonsolderable layer 11, a layer 13 to which solder adheres,and a layer 15 of solder adhered to the top of the layer 13. A hole 17extends through the entire member 9. The member 9 may be welded by meansof end 11 to a support and the solder end 15 used to form a solderedattachment to a device to be supported.

The variety of materials forming the composite will be clear from thefollowing:

Strip 1 of the FIG. 3 clad metal article may be formed from solderablenickel, copper, brass, et cetera. Strip 3, on the other hand, may beformed of nonsolderable stainless steel, Kovar, aluminum, cobalt ornickel base alloys, titanium, zirconium, or other suitable metals oralloys which reject solder material. The solder layer 5 may be anysuitable solder which can be applied to layer 1 by a hot-dippingprocess, as, for example, a conventional leadtin-antimony alloy.

A composite clad metal article comprising a nickel strip 1 bonded to astainless steel strip 3 and faced with a solder comprising aconventional lead-tin-antimony alloy has been found satisfactory for themanufacture of base tabs for transistors. The ratio or thicknesses ofthe various metals is variable, depending on the ultimate desired finalluse. For example but without limitation, strip or layer 1 may constituteabout of the thickness of the article, layer 3 about 10%, and the solder5a may constitute a thin film.

It should be noted that the nonsolderable material is useful not only asa stop-off during the manufacturing operation but also in itsapplication by preventing the flow of solder material onto the surfaceprotected by the nonsolderable material during the soldering operation.

FIGS. 5 and 6 of the drawings illustrate an embodiment of the inventionwhereby the need for trimming of excess solder from the clad metal iseliminated. As shown in FIG. 5, a strip 19 of a metal which rejectsliquid solder is provided with a shallow groove 21 extending along itsupper surface. The groove 21 is inlaid with a strip 23 of a metal (suchas nickel) to which liquid solder will adhere. The strips 19 and 23 arebonded together by solid-phase bonding or liquid-bonding techniques. Theside edges of strip 23 preferably abut shoulders 25 at the sides ofgroove 21. Then the two strips are run through a liquid bath of hotmolten solder. Strip 19 rejects the solder so that there is no solderadhering to its surfaces when it is removed from the liquid bath.However, a layer 27 of solder is deposited on the exposed upper surfaceof strip 23. While solder 27 is shown projecting above the upper surfaceof shoulders 25 over strip 23, it will be understood that groove 21 canbe sufficiently deep, relative to the thickness of the strip 23, and theamount of solder deposited can be regulated so that the upper surface ofsolder 27 deposited on strip 23 will be either above, below orsubstantially coplanar with the upper surface of the shoulders 25. Also,while only one groove 21 is shown in the base strip 19, it will beunderstood that a plurality of these grooves (or other shapes ofrecesses) may be provided, depending upon the intended use of theresulting clad metal strip. The composition of solder 27 and the metalsused for strips 19 and 23 may be the same as those previously set forth.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:

1. A three-component composite metal strip material from which articlesto be soldered can be punched comprising a strip of readily solderablemetal solid-phase bonded to a strip of nonsolderable metal, and a layerof solder adhered to a single surface of said layer of readilysolderable metal forming an exposed surface of said composite metalmaterial, said strip of nonsolderable metal having a groove extendingalong one face thereof, said strip of readily solderable metal beinginlaid in said groove with said single surface thereof exposed from saidgroove and with portions of said nonsolderable metal extending alongsidesaid single surface.

References Cited UNITED STATES PATENTS 2,777,193 1/1957 Albright et al.29626 2,024,150 12/1935 Davignon 29l96.6 1,959,925 5/1934 Pryde 294811,996,183 4/1935 Walters 29191.6

L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant ExaminerU.S. Cl. X.R.

